1. Field of the Invention
The present invention relates to a curved helical compression spring and a method for producing the same, and more particularly to the curved helical compression spring for use in a strut type vehicle suspension, and to the method for producing the spring.
2. Description of the Related Arts
Various types of helical compression spring have been known heretofore. Among them, is known a compression spring having a coil axis curved in a predetermined direction. In Japanese Utility Model Publication No.48-39290, proposed is a method for forming a coil spring with the center line thereof curved in advance in an unloaded state, and mounting it on the vehicle in such a state that the center line is straightened, to produce a moment by the reactive side force of the spring. Also disclosed in British Patent No.1198713 is a helical spring which is coiled about an arc axis of the unloaded spring, and two support surfaces which extend obliquely at an angle to one another. When the helical spring is fitted between the parallel plates, and the longer surface line of the unloaded helical spring faces the outside of the vehicle, the outer half of the helical spring is compressed to a greater extent than the half which faces the inside of the vehicle.
Furthermore, a wheel suspension having a helical compression spring, the center line of which has an approximately S-shaped course in an unloaded state, has been proposed in Japanese patent No. 2642163, which corresponds to U.S. Pat. No. 4,903,985. The suspension was aimed to enable reduce a side force applied to a piston rod of a shock absorber to a great extent, in view of the fact that because tires are becoming wider and wider, hence shifting the wheel-to-road contact point outward, larger and larger angles between the line of support action and the shock absorber axis arise, so that the helical compression spring can not be positioned as obliquely with respect to the shock absorber axis as would actually be desired. In FIG. 5 of the Japanese patent No. 2642163, there is disclosed a compression spring to be compared with the present invention, the center line of which is curved in an unloaded state, and about which it is stated that the radius of curvature of the spring center line is constant and the center line is curved on only one plane, and that the line of the spring action is merely shifted from the center line of the helical spring, so that it is difficult to reduce the side force sufficiently. In other words, it has been concluded that the helical compression spring with its center line curved in the unloaded state is not to be employed.
In any of the publications as mentioned above, a structure of the helical compression spring having a coil axis formed to be curved in a predetermined direction, i.e., a curved helical spring, has not been disclosed, nor a method for producing the same has been disclosed. If the curved helical spring is produced on the basis of a prior cylindrical type of the helical compression spring, for example, it may be produced by varying the pitch of the spring between the inside and the outside of the curved plane. Therefore, the pitch of the curved helical spring will be varied alternately in dependence upon the number of coils, along the coil axis. However, it is very difficult to produce the compression spring for creating a predetermined side force, holding it in a predetermined curved shape, by varying the pitch of the spring between the inside and the outside of the curved plane. Therefore, it is presumed that the helical compression spring with its center line curved in the unloaded state was not to be employed, and it was proposed to employ the S-shaped center line according to the Japanese patent No. 2642163.
In the mean time, there exists a helical spring that is formed to vary a diameter of each coil along the coil axis, such as a truncated cone-shaped helical spring, a barrel-shaped helical spring, or the like. However, it is hardly assumed to employ the helical spring having the varying diameter of the coil, with its coil axis curved, for the helical compression springs as disclosed in the prior publications. It is natural to be considered that the cylindrical helical compression spring was formed, with the pitches thereof varied between the outside and the inside of the curved plane, because there is no disclosure about such a specific spring that the diameter of the coil is varied along the coil axis, for example, in any of the publications as described above.
Accordingly, it is an object of the present invention to provide a curved helical compression spring for applying a desired side force to a strut of a vehicle suspension appropriately, when mounted on a vehicle.
And, another object of the present invention is to provide a method for producing the curved helical compression spring easily.
In accomplish the above and other objects, a curved helical compression spring according to the present invention includes a plurality of coils along a curved coil axis. Each coil constituting the helical compression spring is increased and decreased in diameter, and the order of the increased diameter and the decreased diameter of each coil is reversed at a predetermined position on the longitudinal axis of the helical compression spring. Thus, the curved helical compression spring according to the present invention has the curved coil axis, such as the coil axis curved in C-shape.
The helical compression spring may be formed in such a manner that each coil constituting the coils between one end of the helical compression spring and the predetermined position is increased in diameter and then decreased in diameter, and that each coil constituting the coils between the predetermined position and the other one end of the helical compression spring is decreased in diameter and then increased in diameter. More practically, one section of each coil having approximately a half of the circumference of each coil divided by a plane including the coil axis may be increased in diameter, whereas the other one section of approximately a half of the circumference of each coil may be decreased in diameter.
The method for producing a helical compression spring having a plurality of coils along a curved coil axis, may comprise the steps of forming each coil constituting the helical compression spring to be increased and decreased in diameter, and reversing the order of forming each coil to be increased in diameter and decreased in diameter at a predetermined position on the longitudinal axis of the helical compression spring.
In the method as defined above, each coil constituting the coils between one end of the helical compression spring and the predetermined position may be formed to be increased in diameter and then decreased in diameter, and each coil constituting the coils between the predetermined position and the other one end of the helical compression spring may be formed to be decreased in diameter and then increased in diameter.
Preferably, one section of each coil having approximately a half of the circumference of each coil divided by a plane including the coil axis is formed to be increased in diameter, and the other one section having approximately a half of the circumference of each coil the spring is formed to be decreased in diameter.
In the case where an appropriate side force is to be applied, when the curved helical compression spring as constituted above is mounted on a strut-type vehicle suspension, it is necessary to provide a relative relationship between the shape of the curved helical spring in its unloaded state, and an upper seat and/or a lower seat to be mounted thereon, as described hereinafter. In any case, when the curved helical compression spring as constituted above, such as the curved spring having a C-shaped coil axis, is employed, that relationship may be provided easily.
Firstly, the curved helical compression spring is disposed between the upper seat and the lower seat, with the upper seat an/or lower seat tilted by a predetermined angle. For example, the helical compression spring is mounted on the lower seat tilted in the direction for shortening the longitudinal length of the spring at the outside of the curvature of the spring in its unloaded state, and/or it is mounted on the upper seat tilted in the direction for shortening the longitudinal length of the spring at the inside of the curvature of the spring in its unloaded state.
Secondly, the upper seat and the lower seat are held in parallel without being tilted, and the pitch of an upper end coil and/or a lower end coil of the C-shaped curved helical compression coil is set to tilt the end plane of the upper end coil and/or the lower end coil at a predetermined angle against the upper seat or the lower seat to be seated. For example, the pitch of the lower end coil may be set to tilt the end plane of the lower end coil at a predetermined angle against the lower seat to be seated, in the direction for shortening the longitudinal length of the spring at the inside of the curvature, and/or the pitch of the upper end coil may be set to tilt the end plane of the upper end coil at a predetermined angle against the upper seat to be seated, in the direction for shortening the longitudinal length of the spring at the outside of the curvature.
Thirdly, the upper end coil and/or the lower end coil of the C-shaped curved helical compression spring are arranged to be offset. For example, the center of the end plane of the upper end coil may be arranged to be offset to the center of the end plane of the lower end coil in the direction of the inside of the curvature of the spring. Or, the center of the end plane of the lower end coil may be arranged to be offset to the center of the end plane of the upper end coil in the direction of the outside of the curvature of the spring. Accordingly, when the curved helical compression spring is disposed between the upper seat and the lower seat arranged in parallel with each other, can be obtained the same effect as those obtained in the case where the pitch of the upper end coil and/or lower end coil is set to tilt the end plane of the upper end coil and/or lower end coil at a predetermined angle against the upper seat and/or lower seat.